Gaussian 03 Online ManualLast update: 2 October 2006 | |

## GVBThis
method keyword requests a perfect-pairing General Valence Bond (GVB-PP) calculation.
GVB requires one parameter: the number of perfect-pairing pairs to split; for
example: ## INPUT FOR GVB CALCULATIONSNormally most of the difficult input for a GVB-PP calculation involves specifying the initial guess. (Link 401). This often includes alteration of orbitals to ensure the correct identification of high-spin, perfect-pairing, and closed-shell orbitals and possible reduction of SCF symmetry to account for the localized orbitals which usually represent the lowest energy solution for GVB-PP. The GVB program reads the number of orbitals in each GVB pair (in
format 40I2). The number of lines read is fixed (and normally 1), so no terminating
blank line is needed. For a molecule having spin multiplicity S, N GVB pairs,
and The S-1 highest occupied orbitals in the initial guess, which would have been singly occupied in an ROHF calculation, become high-spin orbitals. The next lower *N*occupied orbitals, which would have been doubly occupied in an ROHF calculation, become the first natural orbitals of the GVB pairs.Any remaining orbitals occupied in the guess stay closed-shell. The lowest *n*_{1}-1 virtual orbitals become natural orbitals 2 through*n*_{1}of the first GVB pair, then the next*n*_{2}-1 orbitals are assigned to pair 2, and so on. The GVB-PP scheme does not allow an orbital to be shared by more than one GVB pair.Any remaining (virtual) orbitals from the initial guess become virtual orbitals in the GVB calculation.
Generally
If
the number of orbitals in a pair is negative, the root of the CI to use for that
pair and the pair's initial GVB coefficients are read in format (I2,5D15.8). This
is useful if a
Combining several orbitals with the
same
Energies, analytic gradients, and numerical frequencies. Here is a GVB(3/6) calculation performed on singlet methylene: # GVB(3)/6-31G(d) Guess=(Local,LowSym,Alter) Pop=Full Test GVB(3) on CH2
The perfect pairing GVB method includes the effects of The There are 4 symmetry adapted basis functions of A1 symmetry. There are 0 symmetry adapted basis functions of A2 symmetry. There are 1 symmetry adapted basis functions of B1 symmetry. There are 2 symmetry adapted basis functions of B2 symmetry. Thus for C 1 4 0 2 3 9 Since this information always requires exactly one line, no blank line terminates this section. The order of orbitals
generated after localization by the initial guess in the first job step was C-1s
C-H Finally, the one line of input to the GVB code indicates that there are 2 natural orbitals in each of the 3 GVB pairs. |